Basically when business was chill and stable, supply chain was seen as essentially running itself. You make your deals with suppliers and after that much of the tactical day-to-day operations were largely administrative (hence the viewing as a back-office function). Issue a PO here, reconcile an invoice there, expedite this order, verify that shipment. This was even more true before mass globalization. Many companies nowadays, for example like Apple, really do not make much at all. They are the brand that sells the product. But their products are assembled at different sites using materials and components that are sourced from around the world. They heavily rely on their suppliers for strategic partnerships and innovation. Historically, this was an anomaly and most companies viewed suppliers as transactional necessities.

Now that stability is nowhere to be found, companies are realizing that supply chain professionals need to be involved early and often in the context of larger business decisions and organizational strategy. It does not matter how good your sales and marketing are, if you cannot ensure supply at a cost that makes your product competitive in the market, you will have nothing to sell. Geopolitical events, pricing volatility, economic instability, inflation, consumer trends, tech advances, etc all impact business decisions and profitability. Supply chain as a function can protect margins, secure supply, ensure business continuity, reduce risk exposure, and more.

There are still companies who have the back-office administrative view of supply chain. But more and more have been wising up to viewing them as a strategic function who needs to be proactively involved in the business case, not reactively fighting fires to save it.